BTW, would anyone like to speculate on the unique benefits of a mirrorless A-mount (not E-mount) design?

Not sure what unique benefits a mirrorless A-mount could have that wouldn't be equally possible in an E-mount design. The cameras could essentially be identical, except for a different physical mount.

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Rather than address each of these points, let me jump to the punch line: It appears to me that anything that could be done with a mirrorless A-mount camera - including sensor shift stabilization - could also be done with a mirrorless E-mount camera designed to the same specs and provided there is an optional LA-EAx adapter for some specific needs.

Let's imagine a mirrorless A-mount A99 and call it the M99... and also imagine an E-mount version of that and call it the E99. The E99 could have the same form factor, use the same battery and grip and other accessories, and offer all the same features as the A-mount version. We already know standard PDAF could be provided by the LA-EA2. Sensor shift stabilization should also be possible in that camera because the sensor itself could be located further toward the front than current NEX models, and with the E-mount also moved correspondingly further forward. Then more usable space opens up behind the sensor. Looking toward the future, any hypothetical advantages offered by the empty space in the M99 could be accommodated with some other specialized adapter.

Considering all this, the advantage of the M99 is that no adapters would be needed for A-mount lenses, so it would be simpler and smaller and cheaper - but for A-mount users only.

The advantage of the E99 would be that native E-mount lenses would be supported - and also all the other lenses now supported by E-mount incuding A-mount lenses through the use of adapters.

BTW, I'm not saying I personally want or need either of these cameras. Just talking about what's possible.